Elastomeric materials have long been used as gaskets, seals and other like components of architectural structures, vehicles, appliances and other such articles of manufacture. For example, in the field of architecture, elastomeric architectural strips are used to cover joints between building sections, at roof lines and around windows, both in new construction and as a repair item for preexisting buildings. Silicone polymers are particularly important in the fabrication of architectural strips. These polymers are extremely flexible and strong, and their inertness makes them resistant to oxidation and photodegradation. Silicone rubbers may be fabricated in a variety of colors by the inclusion of pigments therein, so as to match a variety of substrates.
A wide variety of elastomeric articles, such as architectural strips, gaskets and the like are frequently prepared from silicones or other polymeric compositions by a process in which resin composition is extruded to provide a shaped body which is subsequently cured to produce the finished item. In the context of the present disclosure, an extrusion process is defined to include any forming process wherein a precursor of the elastomer is forced under pressure into or through a shaping member such as a die or a mold to produce a shaped body. A number of shaping processes are known in the prior art. For example, U.S. Pat. No. 4,783,289 discloses a continuous extrusion process for the preparation of elongated silicone rubber members. According to the process, a silicone composition is extruded from a die into a body of water to produce an elongated member which passes through the body of water, and cures while it is doing so.
Elastomeric articles produced through extrusion processes of the prior art tend to cure with a very smooth surface. In many instances, this smooth surface is not desirable in the article. For example, in architectural applications, it is generally desirable that joints and seals blend in with the appearance of the building, and the glossy surface of the elastomer contrasts strongly with the texture of stone, wood, concrete and other such building materials. In some instances, it is desirable to apply paint or other coatings to an elastomeric body, and such coatings often adhere poorly to a highly glossy surface. For reasons such as these, the prior art has made various efforts toward providing a matte finish on extruded elastomeric items. For example, a matte finish can be provided to an item by curing the elastomer within a mold having a textured surface. This approach is impractical when very large, or long, items such as architectural strips are being fabricated, or when the residence time of the article in the mold is a factor in the logistics or economics of the molding process. In another approach, a textured surface is provided to the cured article by brushing, sanding or otherwise abrading the surface. This approach constitutes an additional processing step and is not always practical, particularly when the items being manufactured have large or complex, surfaces. In yet another approach, the finished articles are provided with a textured surface by overcoating them with another material. Again, this requires a complicated post-processing step, and the technique often is not applicable when the item includes surface characteristics which would be masked by the top coat.
It will be appreciated that there is a need for a process by which elastomeric articles, particularly silicone rubber elastomeric articles, having a matte finish may be fabricated. The process should not require any post-cure processing steps nor should it require any long residence time of the article in a shaping die or mold during the curing process. It is further desirable that any such technique be compatible with continuous fabrication processes such as those used for the extrusion of silicone rubber strips. It is also desirable that any such technique not require extensive modification of presently employed processing equipment.
The present invention is directed to a process for the manufacture of elastomeric articles having a matte finish. The process is particularly suited for the fabrication of silicone rubber articles and may be implemented in a continuous fabrication process, such as that used for the manufacture of elongated architectural strips. The method of the present invention is simple to implement and control, and provides high quality, matte finished, cured, elastomeric articles. These and other advantages of the present invention will be readily apparent from the drawings, discussion and description which follow.